Chemokine receptors belong to the most druggable class of receptors and modulate immune responses central to a wide variety of disease states ranging from inflammation and autoimmunity to viral infection, asthma and cancer, making these receptors prime drug targets. In spite of their apparent therapeutic tractability, numerous clinica trials of seemingly promising compounds have met with limited success. A unique challenge in chemokine drug discovery is the complexity of ligand- receptor interactions, with many chemokine ligands binding to multiple receptors and many receptors responding to numerous chemokines. These overlapping features make it difficult to clearly identify single receptors or ligands as drug targets, and to achieve therapeutic efficacy by targeting a single protein. Furthermore, it is now appreciated that although several chemokines may activate the same receptor, the nature of the transduced signals can vary dramatically between ligands. Thus, not only is the ability to define the selectivity of the ligands across the range of chemokine receptor vitally important, but also the ability to measure the intensity, duration, and final outcome of th signals that are produced. With 20+ chemokine receptors, 45+ ligands, and multiple downstream readouts, measuring the matrix of possible phenotypes with standard techniques is time and cost-prohibitive. In Phase I studies, we developed a functioning multiplex assay platform for receptor internalization that enabled nine chemokine receptors to be screened simultaneously in a single assay well. In this Phase II proposal we will create two multiplex panels containing 18 human or murine chemokine receptors and expand the number of assay readouts to include calcium signaling, receptor desensitization, and chemotaxis. The system will be used to create a comprehensive ligand-receptor interaction database of all naturally-occurring chemokines and to discover synthetic chemokine ligands with non-natural profiles of selectivity and signaling. These results will provide the basis for commercialization of this technology as a drug discovery platform for the identification of compounds with unique selectivity profiles for treatment of inflammation, autoimmunity and other chemokine-mediated diseases.